Written with contributions by Emmanuel Byamukama, former SDSU Extension Plant Pathologist.
About Fairy Rings
Seeing greener grass in circular pattern in your lawn (Figure 1)? This is not due to uneven fertilizer application but rather due to a fungi feeding on decomposing matter (old tree stumps, leaves or roots) and releasing nitrogen in the affected areas.
The name “fairy ring” comes from a medieval belief that these developed in the grass after fairies danced in the area! The pattern starts as a small circle, and over time, it grows outward as fungal mycelia spread in the soil. In wet, cool weather, these affected areas may develop fruiting bodies (mushrooms). Do not eat such mushrooms, as they are poisonous.
Fairy rings do not usually kill grass and may disappear on their own over time. Aerating the lawn, collecting the clippings to reduce thatch build-up and fertilizing the lawn can help minimize the occurrence.
If you are especially concerned with the uneven greenhouse, you could remove the soil from the affected area, add new soil and reseed.